Field of the Invention
The invention relates to a mark configuration for the orientation and/or determination of the relative position of a substrate and/or of layers on the substrate during a lithographic exposure. The mark configuration can be formed on a wafer for the production of dynamic random access memories.
During the fabrication of semiconductor components, structures are formed in different planes, which are applied successively on a substrate and then altered in each case by further processing steps. The processing steps include e.g. deposition steps, photomasking steps, resist development and resist patterning steps.
As a result of the ever decreasing dimensions of the structures, it is necessary for sequentially applied layers to be oriented exactly to one another, since otherwise the function of the semiconductor components is not ensured.
The structures are fabricated using an exposure tool, the exposure acting on a photosensitive resist (photoresist) that is applied to the substrate (e.g. wafer). The substrate is loaded into the exposure tool. Using alignment marks on the substrate, the exposure tool identifies defined positions. The substrate is oriented and exposed on the basis of the values determined using the alignment marks. The exposure produces structure alterations in the photoresist, which are transferred to a structure in the semiconductor component in subsequent processing steps.
Special measurement marks in the photoresist are used to determine whether the orientation of the layers has been performed with sufficiently high register accuracy. If the register accuracy is not sufficient, then the resist layer can be removed again. A new exposure with a new orientation of the substrate then takes place (rework).
One possibility for identifying the position of the marks consists in an optical evaluation. To that end, monochromatic or white light is radiated onto the substrate and the reflected light is evaluated e.g. by an image identification. In this case, the efficiency of the evaluation depends on the differences in contrast in the image. In this case, the contrast is defined as the ratio of the difference between the maximum and minimum intensity to the sum of the maximum and minimum intensity.
Usually, the differences in contrast on the substrate are produced by step heights or varying reflectivity of mark structure and surroundings.
However, these differences in contrast often do not suffice to enable an evaluation and thus a good orientation or checking of the substrate.
Moreover, an unfavorable sequence of the processing steps, e.g. a CMP step carried out beforehand, can impair the difference in contrast between the mark and the surroundings.
It is accordingly an object of the invention to provide a mark configuration, a wafer with at least one mark configuration and a method for the fabrication of the mark configuration which overcome the above-mentioned disadvantages of the prior art devices and methods of this general type, such that an orientation of layers and/or of the substrate is possible in a simple and efficient manner.
With the foregoing and other objects in view there is provided, in accordance with the invention, a mark configuration for orientation and/or determination of a relative position of a substrate and/or layers on the substrate during a lithographic exposure. The mark configuration contains a patterned background in or on the substrate, and a mark having at least one part disposed above the patterned background. The mark increases a difference in contrast between the mark and the substrate.
By virtue of the fact that at least one part of a mark is disposed above a patterned background, the contrast of the mark relative to the substrate is improved.
In one advantageous refinement of the mark configuration according to the invention, a first mark, in particular as an alignment mark or part of a measurement mark in a first layer, is disposed above the patterned background. An alignment mark serves for orienting the substrate during an exposure in an exposure tool. However, the first mark may serve as part of a measurement mark, together with marks applied later, for enabling a relative orientation of layers with respect to one another. In this case, the improved contrast always allows a better identification of the position of the substrate or of the layers on the substrate.
It is also advantageous if a second mark, as a measurement mark or part of a measurement mark in a second layer, in particular a photoresist layer, is disposed above the patterned background, the second mark being disposed in such a way that the orientation of the second layer with respect to the first layer can be quantitatively detected. As a result, after an exposure, it is possible to detect whether the latter has been performed correctly.
An advantageous mark configuration is also present if the first mark is configured as an alignment mark that forms a measurement mark together with the second mark. As a result, the alignment mark is used doubly, thereby obviating the provision of a first part of a measurement mark.
In order to increase the contrast, it is advantageous if the patterned background is disposed below the entire extent of at least one of the marks.
In one advantageous refinement of the mark configuration according to the invention, the patterned background has a regular, in particular a linear or grid-shaped, pattern. Such patterns can be fabricated relatively easily and the marks stand out well against the patterned background.
It is advantageous if the patterned background has at least one element whose reflectivity differs from that of the substrate. Differences in the reflectivity enable an efficient evaluation by light irradiation of the substrate. It is also advantageous if the patterned background has at least one elevation made of an oxide layer, monocrystalline silicon, polysilicon, aluminum and/or copper, since these elements, too, can be readily detected during an irradiation.
One embodiment of the mark configuration according to the invention advantageously has a patterned background with at least one depression, in particular a trench, a deep trench, and/or a multiplicity of holes. Altering the absorption by depressions also makes it possible to improve the efficiency of detection of the marks.
In this case, it is also advantageous if the pattern of the patterned background extends parallel to an axis, in particular the longitudinal axis of one of the marks, and/or perpendicular to the longitudinal axis of the mark.
Furthermore, it is advantageous if the dimensions of the individual elements of the patterned background lie below the resolution limit of a measuring apparatus for the detection of the marks.
For an efficient fabrication of the semiconductor components it is advantageous if at least one mark is disposed in a layer below the layer that is currently to be processed.
In the manufacture of the mark configuration, first a patterned background is fabricated on or in a substrate, in particular a semiconductor material, and then at least one part of a mark is disposed above the patterned background. This serves for producing an increased difference in contrast between mark and substrate.
In this case, it is advantageous if a first mark, in particular as an alignment mark or part of a measurement mark in a first layer, is disposed above the patterned background. Preferably, a second mark, as a measurement mark or part of a measurement mark in a second layer, in particular a photoresist layer, is also disposed above the patterned background.
A particularly effective improvement of the differences in contrast results if the patterned background is introduced as a regular, in particular a linear or grid-shaped, pattern onto and/or into the substrate. In this case, it is advantageous if at least one element of the patterned background whose reflectivity differs from that of the substrate is applied to the substrate. It is also advantageous if, for the patterned background, at least one elevation made of an oxide layer, monocrystalline silicon, polysilicon, aluminum and/or copper is applied to the substrate. In an advantageous manner, for the patterned background, at least one depression, in particular a trench, a deep trench, and/or a multiplicity of holes is introduced into the substrate.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a mark configuration, a wafer with at least one mark configuration and a method for the fabrication of at least one mark configuration, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.